Established of Trypanosoma cruzi - the etiologic agent of Chagas' disease- in mammalian hosts depends upon the entry of the invasive trypomastigote into host cells. Knowledge of the mechanisms that enable these forms of the parasite to penetrate host cells is scare and critical to developing rational strategies for blocking the disease. The long term objective of this proposal is to understand how trypomastigotes invade host cells. To accomplish this goal, specific ligands on the surface of the parasite, involved in its interaction with cells have to be defined, since the parasite cell surface has been implicated in this process. This application proposes to identify these molecules by using as a model trypomastigote clones that vary dramatically in their cell invasive abilities (highly and weakly infective). By studying the cell surface patterns of these distinct clones, it will be possible to identify those molecules involved in host cell invasion. The specific aims of this proposal are: (a) to identify qualitative and quantitative differences in the cell surface of both types of trypomastigote clones by inspecting plasma membrane patterns resolved by one and two dimensional gel electrophoresis, blotted onto nitrocellulose and probed with labeled cell membranes, (b) to isolate these components by affinity chromatography with monoclonal or polyclonal antibodies, that inhibit parasite attachment and internalization into host cells, and to characterize the isolated ligands, (c) to study the capacity of the parasite ligand to inhibit host cell invasion by the parasite; and the potential of the ligand for producing a vaccine that induces a protective immune response in mice against challenge with insect-derived trypomastigotes. The significance of this study is in (a) understanding how T. cruzi, an obligatory intracellular parasite, enters the host cell, and (b) furnishing a model for the invasion process of other intracellular parasites of man.